1. Technical Field of the Invention
The present invention relates to promoting desquamation of the skin and/or stimulating epidermal renewal and/or combating skin aging by topical application thereto of at least one hydroxystilbene compound/composition.
The compounds/compositions of this invention are especially well suited for promoting desquamation of the skin and/or stimulating epidermal renewal and/or combating intrinsic and/or extrinsic skin aging, as well as for nontherapeutically treating the skin to promote desquamation and/or combat skin aging.
2. Description of the Prior Art
Desquamation is a natural phenomenon linked to the fact that the epidermis, which constitutes the upper layer of the skin, is constantly being regenerated. The epidermis consists of several layers of cells, of which the deepest is the basal layer consisting of undifferentiated cells. Over time, these cells will differentiate and migrate to the surface of the epidermis, constituting various layers thereof, until the corneocytes, which are dead cells which are eliminated by desquamation, are formed at the surface of the epidermis. This loss at the surface of the skin is compensated by the migration of cells from the basal layer to the surface of the epidermis. It entails the perpetual renewal of the skin. The forced elimination of the horny layer accelerates epidermal renewal and makes it possible to combat aging.
At the same time, these cells continue their differentiation, of which the last stage is the corneocyte. These are dead cells which constitute the last layer of the epidermis, namely, the outermost layer also known as the stratum corneum.
Skin aging, resulting from the effects of intrinsic or extrinsic factors on the skin, results in the appearance of wrinkles and fine lines, in yellowing of the skin, which develops in particular a shrivelled appearance, possibly accompanied by the appearance of pigmentation marks, in the disorganization of the elastin fibers and of collagen causing a loss of elasticity, suppleness and firmness and in the appearance of telangiectasia.
Certain of these signs of aging are more particularly linked to intrinsic or physiological aging, namely, to "normal" age-related or chronobiological aging, whereas others are more specific to extrinsic aging, namely, aging generally caused by the environment; this is more particularly photoaging due to exposure to the sun, to light or to any other radiation.
The present invention relates to not only intrinsic or physiological aging, but also to extrinsic aging.
Changes in the skin due to intrinsic aging are the consequence of a genetically programmed aging in which endogenous factors are involved. This intrinsic aging causes, in particular, a slowing down of the renewal of the skin cells, which essentially results in the appearance of clinical alterations such as the reduction in the subcutaneous adipose tissue and the appearance of fine wrinkles or fine lines, and in histopathological changes such as an increase in the number and thickness of the elastic fibers, a loss of vertical fibers of the membrane of the elastic tissue, and the presence of large irregular fibroblasts in the cells of this elastic tissue.
By contrast, extrinsic aging causes clinical alterations such as thick wrinkles and the formation of a soft and/or tanned skin, and histopathological changes such as an excessive accumulation of elastic material in the upper dermis and degeneration of the collagen fibers.
Various active agents suggested for combating skin aging are known to this art.
Thus, U.S. Pat. No. 4,603,146 describes the use of retinoic acid and derivatives thereof in cosmetic compositions for combating skin aging.
Moreover, numerous patents and publications (see, for example, EP-A-413528) describe, and numerous commercially available cosmetic compositions include, .alpha.-hydroxy acids such as lactic acid, glycolic acid or citric acid for treating skin aging.
Too, the beta-hydroxy acids and more especially salicylic acid, as well as the derivatives thereof, are known for their desquamative properties (see WO-A-93/10756 and U.S. Pat. No. 4,767,750).
All of the aforesaid prior art compounds elicit action against skin aging by promoting desquamation, namely, the elimination of the "dead" cells situated at the surface of the horny layer of the epidermis. This "desquamative" property is also deemed, often wrongly, "keratolytic" activity.
However, the prior art compounds also present objectionable side effects such as pricking, twitching, overheating and/or redness which are unpleasant for the user.
Need therefore continues to exist for antiaging agents having an action which is at least as effective as that of the prior art compounds, but which do not present the disadvantages thereof.